Support multi-level nested create/update with model `full_clean()`

Description

This implements the core functionality of #604, allowing multi-level create/update of nested resources. It also ensures that model.full_clean() is called before creating a new resource, which ensures that internal information about constraint names doesn't leak out to the client via IntegrityError messages (see #398).

To solve this, we allow update_m2m to recursively call create(), ensuring that the logic for creation of records uses a consistent code path regardless of what depth in the nested data it is created at.

Notes

This is not everything from #604, nor does it fix all of #603. It does fix all of #398. It seemed like #604 was getting too large to review though, so I'm hoping this approach of breaking it up into smaller chunks will work better.

Part of the reason why this approach was a bit easier was that I didn't try to preserve the change from #362. This change didn't come with any tests, has probably been superseded by the key_attr functionality that was added after the fix was merged, and it seems risky to assume that the default behaviour should be to reuse an existing model instance just because some fields match (as pointed out by @bellini666 previously in this comment).

From the changes in this PR, I see several other subsequent bugfixes/improvements that could be made to address the remaining issues from #603 and comments raised in the previous PR #604:

nested creation of OneToOne fields (#603)
Allow key_attr to specify more than one column to perform the lookup on (comment in #604)
Allow key_attr and full_clean/full_clean_options to be specified individually for each type(?) of nested resource specified.
Validation field names should be prefixed with the field name of the nested resource. The format project.milestones.0.name or project.milestones.0.issues.2.tags.3.name could be an option?. Validation errors probably shouldn't stop other nested resources from being created, so all validation errors can be caught and returned at the end. (#404)

Types of Changes

[ ] Core
[x] Bugfix
[ ] New feature
[x] Enhancement/optimization
[ ] Documentation

Issues Fixed or Closed by This PR

Fixes #398
Some of #603

Checklist

[x] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.
[x] I have read the CONTRIBUTING document.
[x] I have added tests to cover my changes.
[x] I have tested the changes and verified that they work and don't break anything (as well as I can manage).

Summary by Sourcery

Implement support for multi-level nested create and update operations with model full_clean() to enhance data integrity and prevent constraint name leaks. Add tests to verify the new functionality.

New Features:

Implement multi-level nested create and update functionality for resources, allowing recursive calls to create nested resources.

Bug Fixes:

Fix issue #398 by ensuring model.full_clean() is called before creating a new resource to prevent leaking internal constraint names via IntegrityError messages.

Enhancements:

Add support for excluding certain many-to-many fields from processing during create and update operations to prevent circular references.

Tests:

Add tests for multi-level nested creation and update mutations to ensure the new functionality works as expected.

Reviewer's Guide by Sourcery

This PR implements multi-level nested create/update functionality for resources and ensures proper model validation through full_clean(). The implementation focuses on allowing nested resource creation at any depth while maintaining consistent code paths and proper validation.

Sequence diagram for multi-level nested create/update

sequenceDiagram
    actor User
    participant Client
    participant Server
    participant Database

    User->>Client: Initiate create/update request
    Client->>Server: Send GraphQL mutation
    Server->>Database: Validate data with full_clean()
    alt Validation passes
        Server->>Database: Create/update nested resources
        Database-->>Server: Return success
        Server-->>Client: Return success response
    else Validation fails
        Server-->>Client: Return validation error
    end

Updated class diagram for mutation resolvers

classDiagram
    class MutationResolver {
        +create(info, model, data, key_attr, full_clean, pre_save_hook, exclude_m2m)
        +update(info, model, data, key_attr, full_clean, pre_save_hook, exclude_m2m)
        +_create(info, manager, data, key_attr, full_clean, pre_save_hook, exclude_m2m)
        +update_m2m(info, instance, field, value, key_attr)
    }
    class ProjectInputPartial {
        +name
        +milestones
    }
    class MilestoneInputPartial {
        +name
        +issues
    }
    class MilestoneIssueInputPartial {
        +name
        +tags
    }
    MutationResolver --> ProjectInputPartial
    ProjectInputPartial --> MilestoneInputPartial
    MilestoneInputPartial --> MilestoneIssueInputPartial

File-Level Changes

Change	Details	Files
Added support for multi-level nested resource creation and updates	Modified update_m2m to recursively handle nested resource creation Added reference instance data to prevent circular references Implemented consistent creation path through _create helper function Added exclude_m2m parameter to prevent circular references in nested creation	`strawberry_django/mutations/resolvers.py`
Added model validation through full_clean()	Ensured full_clean is called before creating new resources Added validation error handling to prevent leaking internal constraint names	`strawberry_django/mutations/resolvers.py`
Added comprehensive test coverage for nested mutations	Added tests for multi-level nested creation Added tests for multi-level nested updates Added tests for nested model validation Added test cases for shared resource references	`tests/test_input_mutations.py`
Extended schema to support nested mutations	Added MilestoneIssueInputPartial type for nested issue creation Added create_project_with_milestones mutation Updated MilestoneInputPartial to support nested issues	`tests/projects/schema.py`

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#398	Perform validation check on nested fields when they are updated via the parent field	✅

Possibly linked issues

#603: The PR implements multi-level nested create/update, addressing the issue's core functionality.
#398: PR fixes issue by ensuring full_clean() is called during nested updates, addressing validation.
#383: The PR implements multi-level nested updates, addressing the issue's request for nested relation updates.

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strawberry-graphql / strawberry-django